phil-kaddy avatar image
phil-kaddy asked

Tesla Model S Batteries without BMS

Hi Victron Community,

I am currently setting up a grid parallel ESS with a Multiplus 2, a Venus GX and two 5KWh Tesla (24V each) Modules in series. I will setup a BMS (SimpBMS) for the Batteries in the future but would like to use them beforehand (with restricted parameters of course to ensure that they don't under and overcharge ).

I am struggling to find a battery option in VE-Config and on the Venus Remote to tell the multiplus to charge/discharge the batteries according to voltage. All options in the ESS Assistants appear to be requiring a BMS communicating to the GX/Multi that batteries are charged/discharged.

Isn't there a simple option where I can set the Multiplus to charge the Batteries up to 48V max and invert down to 38V, for example?

After starting the ESS Assistant I have changed the inverter and charger settings in Ve-Config manually to the above (38V - 48V), but the system does not engage and appears to be waiting for a signal from a (non-existent) BMS.

Is there a "BMS off" or "No BMS" function (or similar) on the GX that I have overlooked? Any help would be much appreciated.

Many thanks

Schematics of my setup are below:

Multiplus-IIbattery chargingESSBMSVenus GX - VGX
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2 Answers
Meine_Energiewende avatar image
Meine_Energiewende answered ·

Hi Kaddy,

i have nearly the same setup running. 2 x Tesla in series with a multiplus II and a fronius pv inverter on ac-in. You should be able to set the "batterie monitor" to "multiplus II" under -> system setup.

I already have a simpbms running.

At the moment there are some limitations. The Multi is only able to invert down to 41.2 volts. The tesla batteries would be able to run down to 39 Volts (upper save endurance limit is 49.2 Volts).

The possbile usable capacity is limited by this to 70 % of the 11.2 kW available.

Hope it helps.


PS: i would strongly recommend to use the system with a bms only -> in combination with an dc trip breaker. If some of the cells have a thermal problem (or internal resistance), you will be on the save side ....... otherwise this could lead to a thermal runaway.

Even the balancing of the tesla cells is only working if the bms is telling them to balance :)

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littlewiggler avatar image littlewiggler commented ·

Was the SIMP-BMS pretty much plug and play after you set the battery params?

Did you make any changes to a possible CCX or BMV-712?

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Meine_Energiewende avatar image Meine_Energiewende littlewiggler commented ·

Sorry .... missed this message.

SimpBMS is made to be working with a CCX. A BMV is not necessary -> you will see two battery monitors in the CCX and only one is needed.

And no: no changes on any devices.


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phil-kaddy avatar image
phil-kaddy answered ·

Many thanks Jens. This has been most helpful!

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